fix(main/libgmp): fix building with build-all.sh

[twaik]

Fixes error

checking C++ compiler aarch64-linux-android-clang++  -I/data/data/com.termux/files/usr/include  -fstack-protector-strong -Oz -L/data/data/com.termux/files/usr/lib... no, program does not run
configure: error: C++ compiler not available, see config.log for details
...
configure:10520: checking C++ compiler aarch64-linux-android-clang++  -I/data/data/com.termux/files/usr/include  -fstack-protector-strong -Oz -L/data/data/com.termux/files/usr/lib
Test compile:
configure:10534: aarch64-linux-android-clang++  -I/data/data/com.termux/files/usr/include  -fstack-protector-strong -Oz -L/data/data/com.termux/files/usr/lib conftest.cc >&5
configure:10537: $? = 0
configure:10541: ./a.out || ./b.out || ./a.exe || ./a_out.exe || ./conftest
CANNOT LINK EXECUTABLE "./a.out": library "libc++_shared.so" not found
libc: CANNOT LINK EXECUTABLE "./a.out": library "libc++_shared.so" not found
libc: Fatal signal 6 (SIGABRT), code -6 in tid 952305 (a.out)
libc: failed to spawn debuggerd dispatch thread: Invalid argument
/home/builder/.termux-build/libgmp/src/configure: line 10542: ./b.out: No such file or directory
/home/builder/.termux-build/libgmp/src/configure: line 10542: ./a.exe: No such file or directory
/home/builder/.termux-build/libgmp/src/configure: line 10542: ./a_out.exe: No such file or directory
/home/builder/.termux-build/libgmp/src/configure: line 10542: ./conftest: No such file or directory
configure:10544: $? = 127
failed program was:

int main (void) { return 0; }
configure:10649: result: no, program does not run
configure:10665: error: C++ compiler not available, see config.log for details

Related to #21130.

[twaik]

I will merge it in 36 hours if nobody minds or when it gets 2+ approves.